The effect of sodium nitroprusside on the action of herbicides, protoporphyrinogen oxidase inhibitors, and synthetic auxins

To determine the factors that influence the nature of the effect of the nitric oxide donor sodium nitroprusside on the phytoto x icity of herbicides, we studied the dynamics of nitric oxide and hydrogen peroxide formation when sodium nitroprusside is used separately and in combination with herbicides. Three herbicides with different mechanisms of action were used for the studies: the protoporphyrinogen oxidase inhibitor carfentrazone, the synthetic auxin 2,4-D, the effect of which was increased when used together with sodium nitroprusside, and the carotenoid synthesis inhibitor aclonifen, the effect of which was accelerated, but not increased, when used together with sodium nitroprusside. Oilseed radish plants ( Raphanus sativus var. oleiformis ), which are sensitive to the action of the studied herbicides, were used as the model organism. It was found that treatment of plants with s o dium nitroprusside, carfentrazone, and 2,4-D led to an increase in nitric oxide content in plants on the 1st and 4th days after treatment, while on the 8th day, the nitric oxide content in treated plants did not differ from the control. Treatment of plants with aclonifen did not affect the nitric oxide content in plants over the 8-day period following treatment. When sodium nitroprusside was used in combination with carfentrazone and 2,4-D, the increase in nitric oxide content was more pronounced and prolonged compared to the effect of the herbicides alone. When sodium nitroprusside was applied together with aclonifen, an increase in nitric oxide was also observed compared to the control; however, this increase was smaller in both magnitude and duration co m pared to the application of the nitric oxide donor alone. Treatment of plants with sodium nitroprusside resulted in a decrease in hydrogen peroxide content, while herbicide treatment led to an increase in hydrogen peroxide content in plants. When herbicides were applied in combination with sodium nitroprusside, an increase in hydrogen peroxide content was observed compared to the effect of the herbicides alone. At the same time, this increase was most pronounced for carfentrazone, and less intense and shor t er-lived for 2,4-D and aclonifen. Since the content of hydrogen peroxide in plants decreased under the action of sodium nitropru s side alone, it is likely that the increase in hydrogen peroxide content during the combined application of herbicides with sodium nitroprusside is a consequence of the increased nitric oxide levels. It was concluded that the increase in induced nitric oxide fo r mation is a key factor in the enhanced phytotoxic effect of the herbicides carfentrazone and 2,4-D when used in combination with sodium nitroprusside. The possibility of increasing the phytotoxic effect of individual herbicides through join t use with nitric oxide donor s can be utilized to enhance the effectiveness of crop protection against weeds.